1. Field of the Invention
The present invention relates to an optical disk exclusively used for reproduction which has an optically detectable guide groove in which signals have previously been recorded.
2. Description of the Prior Art
Optical disks are capable of recording or reproducing signals in a non-contact manner by means of a laser beam which is narrowed to a minute spot of light and have therefore attracted attention as high-density large-capacity memories. For this reason, a large number of information recording and reproducing apparatus employing optical disks have appeared on the market. When the use of optical disk devices will have expanded in the future a external memories for computer systems or other similar means, operation systems, ready-made programs and data will be supplied by means of optical disks. In other words, there will be a need for optical disks exclusively used for reproduction. Since optical disks are subjected to reproduction by an apparatus which is capable of effecting both recording and reproducing operations, it will be necessary for optical disks exclusively used for reproduction to be consistently interchangeable with optical disks used for both recording and reproducing operations irrespective of their signal recording format.
Referring to FIGS. 1a and 1b which show an optical disk used for both recording and reproducing operations, the reference numeral 1 denotes an optical disk, 2 a data managing information region, and 3 a data recording region.
Optical disks used for both recording and reproducing operations have a data recording region which is employed to record information and further a data managing information region employed to record the address information in relation to the data recording region in which the information has been recorded. Incidentally, if the respective capacities of these regions have previously been specified, since the relationship or ratio between the amounts of the recorded data and the recorded data managing information changes depending upon the contents and quality of information to be recorded, it may become impossible for either one of the above-described two regions to be used. To cope with such a problem, one type of optical disk used for both recording and reproducing operations has, as shown in FIG. 1a, the data managing information region 2 provided such as to extend from the outermost periphery of the optical disk 1 toward the inner periphery thereof (or the data recording region 3 provided such as to extend from the innermost periphery of the optical disk 1 toward the outer periphery thereof). The other type of optical disk used for both recording and reproducing operations has, as shown in FIG. 1b, the data recording region 3 provided such as to extend from the outermost periphery of the optical disk 1 toward the inner periphery thereof (or the data managing information region 2 provided such as to extend from the innermost periphery of the optical disk 1 toward the outer periphery thereof). In such an optical disk, every time information is recorded, these two regions, that is, the data managing information region 2 and the data recording region 3 gradually extend from the outermost and innermost peripheries of the optical disk 1 toward its inner and outer peripheries, respectively. When the two regions come in contact with each other, the efficiency of use of the recording area on the optical disk 1 reaches its maximum.
If, however, an optical disk exclusively used for reproduction is arranged in a manner similar to that of the above-described optical disk used for both recording and reproducing operations the following problems arise. Namely, since it is possible for an optical disk to store a large amount of data, the optical disk is not filled to its capacity simply by storing the software and other data which the user considers to be necessary, and an unrecorded region 4 in which no data has yet been recorded therefore remains between the data recording region 3 and the data managing information region 2, as shown in FIGS. 1a and 1b.
In an optical disk which has an optically detectable guide groove, if no guide groove is provided in the above-described unrecorded region 4, a reduction in the production cost of the master disk is then possible when manufacturing optical disks. However, problems may arise in terms of tracking and focusing, for example, when the optical head of an optical disk apparatus is positioned in the unrecorded region 4 at the time of starting the operation of the apparatus. Further, the above-described optical disk does not enable counting of the number of tracks, which would exist in the unrecorded region 4 if a guide groove were provided therein, when the optical head moves between the data managing information region 2 and the data recording region 3 across the unrecorded region 4, which fact involves a possible problem when the optical head is fed for a track accessing operation.